1. Field of the Invention
This invention relates generally to a liquid droplet ejection head provided with a filter to remove foreign substances from the liquid, an image forming apparatus including the liquid droplet ejection head, and a method for cleaning the liquid droplet ejection head.
2. Description of the Background Art
In general, a liquid droplet ejection head such as an inkjet head employed in an inkjet-type image forming apparatus includes liquid chambers and multiple nozzles each having a diameter of 10 μm. In the inkjet-type image forming apparatus, foreign substances that inadvertently enter the inkjet head during manufacture or with a liquid such as ink dispensed from an ink cartridge to the inkjet head can cause clogging of the nozzles and irregular ejection of ink droplets from the nozzles, thereby degrading image quality. At the same time, recent improvements in processing performance of such as personal computers and other information processing devices have increased demand for high-speed inkjet-type image forming apparatuses. One way to attain high speed is increasing the number of nozzles provided to the inkjet head. However, an increase in the number of nozzles also requires an improved cleaning unit that removes foreign substances from the ink to provide reliable ejection of ink droplets from the nozzles.
There is known a type of inkjet-type image forming apparatus in which a filter that removes foreign substances and bubbles from ink is provided to a common liquid chamber through which the ink is supplied from an ink cartridge to the nozzles to prevent the nozzles from being clogged. In addition, a cleaning opening from which the foreign substances are discharged is provided downstream from the filter in a direction of flow of the ink.
It is known that the clogged nozzles tend to be found at edges of the inkjet head, as evidenced by the graph shown in FIG. 1. Further, it is known that the foreign substances found at the edges of the inkjet head come from a portion of the inkjet head provided upstream from individual liquid chambers.
The upstream portion of the inkjet head has a three-dimensionally asymmetrical shape that causes stagnation of cleaning liquid during cleaning of the inkjet head. It has been found from fluid simulation results that the inkjet head is filled with the ink from the edges to the center during ejection of ink droplets from the nozzles in the event of irregular cleaning of the upstream portion of the inkjet head. Consequently, foreign substances tend to flow to the edges of the inkjet head, yielding the same results obtained from the past production experiments described above. However, because the cleaning opening is provided to the common liquid chamber in the related-art image forming apparatus, it is difficult to reliably clean inside the inkjet head.
Thus, it is required to provide the cleaning opening to each of the individual liquid chambers in place of the common liquid chamber. However, although providing the filter to the individual liquid chambers is well known, foreign substances are trapped within the individual liquid chambers in such a configuration, thereby possibly reducing yield.